Dynamic vulcanization process for preparing thermoplastic elastomers

Abstract

Described in one aspect is a process for preparing a low durometer thermoplastic vulcanizate composition comprising melt blending one or more thermoplastic polymer(s) with a cross-linkable elastomer under conditions of dynamic vulcanization; adding at or after the start of the melt blending at least one curative agent for the elastomer so as to cross-link the elastomer during the melt blending; introducing process oil into the melt blending before, during and/or after the addition of the curative agent; and, extruding a fully crosslinked thermoplastic vulcanizate having a Shore A Hardness of less than 25.

We claim: 
     
       1. A process for preparing a thermoplastic vulcanizate composition comprising:
 melt-blending from 1 to 18 wt % thermoplastic polymer, based upon the total polymer, a cross-linkable elastomer, at least one curing agent, and a process oil such that the weight ratio of process oil to thermoplastic polymer ranges from 200:1 to 4:1; and 
 isolating a thermoplastic vulcanizate composition exhibiting a level of extractables in room temperature cyclohexane not greater that 6 wt %, the composition having a durometer of less than 25 Shore A; 
 wherein the cross-linkable elastomer is one or more of mono-olefin copolymer elastomers, EPDM or butyl rubber, 
 wherein the thermoplastic polymer is one or more of propylene homopolymers or copolymers having a melt temperature due to isotactic arrangement of propylene derived monomers, as measured by DSC, from 50° C. to 175° C. a density of 0.90 to 0.91 g/cm 3  and a melt flow rate from 0.3 dg/min to 50 dg/min; and 
 wherein the thermoplastic vulcanizate composition consists of the reaction product of the thermoplastic polymer, the cross-linkable elastomer, the curing agent, and the process oil. 
 
     
     
       2. A process for preparing a thermoplastic vulcanizate composition comprising:
 i) melt blending a thermoplastic polymer with a cross-linkable elastomer under conditions of dynamic vulcanization; 
 ii) adding before, at or after the start of the melt blending in step i) at least one curing agent for the elastomer so as to cross-link the elastomer during the melt blending; 
 iii) introducing process oil into the melt blending of i) before, during, and/or after, the addition of the curative agent, wherein the process oil is added in a ratio to the thermoplastic polymer established by the equation:
   (−5.9 Tp+ 365 ≧O   L ≧(−8.9 Tp+ 243),
 
 
 where O L  represents the total process oil level in phr, Tp represents the weight percent, on a total polymer basis, of the thermoplastic polymer and ranges from 1 to 18 wt %; and, 
 iv) extruding a thermoplastic vulcanizate blend of thermoplastic polymer and cross-linked elastomer that upon subsequent cooling has a level of extractables in room temperature cyclohexane of less than 6 wt % of the total weight of elastomer; 
 wherein the thermoplastic polymer is one or more of propylene homopolymers or copolymers having a melt temperature due to isotactic arrangement of propylene derived monomers, as measured by DSC, from 50° C. to 175° C., a density of 0.90 to 0.91 g /cm 3  and a melt flow rate from 0.3 dg/min to 50 dg/min and wherein the thermoplastic vulcanizate composition has a durometer less of than 25 Shore A; and wherein the weight ratio of process oil to thermoplastic polymer ranges from 200:1 to 4:1; and wherein the thermoplastic vulcanizate composition consists of the reaction product of the thermoplastic polymer, the cross-linkable elastomer, the curing agent, and the process oil. 
 
     
     
       3. The process of  claims 1  or  2 , wherein the curative agent is added in amount equal to from 1.6 to 10.0 parts per hundred parts rubber. 
     
     
       4. The process of  claim 1  or  2 , wherein the curative agent is added in an amount from 3.0 to 8.0 parts per hundred parts rubber. 
     
     
       5. The process of  claim 2 , wherein the thermoplastic polymer is present in an amount greater than 1 wt % but less than 12 wt % based upon the total weight of thermoplastic polymer plus elastomer. 
     
     
       6. The process of  claim 5 , wherein the thermoplastic polymer is present in an amount greater than 2.0 wt % but less than 6 wt % based upon the total weight of thermoplastic polymer plus elastomer. 
     
     
       7. The process of  claim 2 , wherein the thermoplastic polymer is or contains a compatibilizer or compatiblizer forming thermoplastic, and wherein the process further comprises:
 v) pelletizing the thermoplastic vulcanizate of step iv); and 
 vi) melt processing the pellets formed in v) with one or more additional thermoplastic polymers. 
 
     
     
       8. The process of  claim 2 , wherein the thermoplastic polymer is or contains a compatibilizer or compatiblizer forming thermoplastic, and wherein the process further comprises:
 v) introducing after cure into the processing one or more additional thermoplastic polymer that may be the same or different than the original thermoplastic polymer. 
 
     
     
       9. The process of  claims 1  or  2 , wherein more than one melt processors is used in melt processing. 
     
     
       10. The process of  claims 1  or  2 , wherein the process oil is added to establish a ratio of oil to thermoplastic polymer of from 150:1 to 5:1. 
     
     
       11. The process of  claims 1  or  2 , wherein the process oil is added to establish a ratio of oil to thermoplastic polymer of from 140:1 to 30:1. 
     
     
       12. The process of  claim 2 , wherein the cross-linkable elastomer consists essentially of one or more of mono-olefin copolymer, EPDM or butyl rubber. 
     
     
       13. The thermoplastic vulcanizate composition that consists of from 1 to 18 wt % thermoplastic polymer, based upon the total polymer, a fully cross-linked elastomer exhibiting a level of extractables in room temperature cyclohexane not greater that 6 wt %, and an oil, where the composition has a durometer less of than 50 Shore A, and where the cross-linked elastomer including one or more of mono-olefin copolymer elastomers, EPDM or butyl rubber, wherein the thermoplastic polymer is one or more of propylene homopolymers or copolymers having a melt temperature due to isotactic arrangement of propylene derived monomers, as measured by DSC, from 50° C. to 175° C., a density of 0.90 to 0.91 g/cm 3 , and a melt flow rate from 0.3 dg/min to 50 dg/min, and wherein the weight ratio of process oil to thermoplastic polymer ranges from 200:1 to 4:1. 
     
     
       14. The thermoplastic vulcanizate composition of  claim 13 , wherein the fully cross-linked elastomer exhibits a level of extractables in room temperature cyclohexane not greater that 2 wt %. 
     
     
       15. The thermoplastic vulcanizate composition of  claim 13 , wherein the thermoplastic polymer is one or more propylene homopolymers. 
     
     
       16. The thermoplastic vulcanizate composition of  claim 13 , wherein the elastomer is an EPDM. 
     
     
       17. The thermoplastic vulcanizate composition of  claim 13 , wherein the thermoplastic vulcanizate consists of from 1 wt % to less than 6 wt % thermoplastic polymer. 
     
     
       18. The thermoplastic vulcanizate composition of  claim 13 , wherein the ratio of oil to thermoplastic polymer is from 150:1 to 5:1. 
     
     
       19. The thermoplastic vulcanizate composition of  claim 13 , wherein the ratio of oil to thermoplastic polymer is from 140:1 to 30:1. 
     
     
       20. The thermoplastic vulcanizate composition of  claim 13 , wherein the thermoplastic vulcanizate composition has a durometer less of than 25 Shore A. 
     
     
       21. The process of  claim 1 , wherein the process oil is added to establish a ratio of oil to thermoplastic polymer of from 200:1 to 10:1. 
     
     
       22. The process of  claim 1 , wherein the process oil is added to establish a ratio of oil to thermoplastic polymer of from 200:1 to 8:1. 
     
     
       23. The process of  claim 1 , wherein the thermoplastic polymer is present in an amount greater than 1% but less than 12 wt % based upon the total weight of thermoplastic polymer plus elastomer. 
     
     
       24. The process of  claim 1 , wherein the thermoplastic polymer is present in an amount greater than 1% but less than 10 wt % based upon the total weight of thermoplastic polymer plus elastomer. 
     
     
       25. The process of  claim 1 , wherein the thermoplastic polymer is present in an amount greater than 1% but less than 8 wt % based upon the total weight of thermoplastic polymer plus elastomer.